probably the paddle wheel/maltese cross/ experiment and other things to show that electrons have wave-particle duality.
the one where there were like 6 vertical vacuum tubes with different pressures to show how pressure inside the tubes affect the luminosity.
then there was the one where the stopping voltage can be modified to prevent electrons in the vacuum tube reaching from one electrode to another.
from my memory.
also, here's a safety tip that can help you and yourself in the exam for 1 mark:
stay the fuck away from vacuum tubes in operation because they give off invisible x-rays